An example of a known glycopeptide antibiotic is vancomycin, which contains a disaccharide substituent linked to a heptapeptide structure. See Malabarba A., et al., Med. Res. Rev., 17(1):69-137 (1997a); Nagarajan R. et al., J. Chem. Soc. Chem. Comm. 1306-1307(1988); Nagaranjan R., Antimicr. Agents Chemother., 35:605-609 (1991); and Nagaranjan R., J. Antibiotics, 46:1181-1195 (1993). Vancomycin is effective against gram positive bacteria. However, vancomycin resistant strains have been recently observed, thus increasing the need for new and effective therapeutic agents.
The glycopeptides of the present invention are useful against many gram positive microorganisms, including vacomycin resistant enterococcus (VRE), methicillin resistant Staphylococcus aureus (MRSA), methicillin resistant Staphylococcus epidermidis (MRSE), and methicillin resistant coagulase negative Staphylococci (MRCNS). The antibacterial compounds of the present invention thus comprise an important new contribution to the development of therapeutic regimens for treating infections caused by these difficult to control pathogens and resistant strains.
There is an increasing need for agents effective against such pathogens, which are at the same time relatively free from undesirable side effects. Moreover, the physicochemical and pharmacological characteristics of candidate drugs, including their solubility, charge, hygroscopic characteristics, lipophilicity, bioavailability, tissuc distribution, serum half-life and the like can play important roles in determining the success or failure of a candidate drug in the clinic. For example, it has been reported that a vancomycin analog in the Phase III clinical studies, which bears a chlorophenylbenzyl (also referred elsewhere in this application as chlorobiphenyl; other substituents are described in, e.g., Rodriguez, M. J., J. Antibiotics, 51(6):560-569 (1998)) substituent on the amine nitrogen of vancosamine and a free hydroxyl group on the C-6 position of glucose, exhibits a serum half-life in excess of two weeks. It has also been reported that traces of this vancomycin analog can be detected in patients up to a year after drug administration. Clearly, should a patient experience any adverse reaction to any drug, it would be beneficial if the patient's body could metabolize and/or clear the drug relatively quickly, e.g., within about 24 or less, preferably within about 12 hours or less, most preferably within about 6-8 hours or less.
It should be noted that antibiotics of the type that include vancomycin are typically administered parenterally, that is intravenously. Hence, a relatively high clearance rate would not typically be a disadvantage, and as stated above, would be of potential great benefit to certain patients. Such intravenous formulations impose certain requirements on a drug, not the least of which is adequate solubility in the formulation medium. Thus, poorly soluble drugs may be unsuitable as a practical matter because the clinician is unable to dissolve the drug in a formulation, much less deliver adequate amounts of the drug via intravenous drip. Generally, the pH of the formulation is buffered to correspond to physiological pH, which is about 7.4. While some leeway is possible in the pH of an intravenous formulation, pain at the site of injection typically limits the useful range of pH to no less than about 5 to no greater than about 8. Preferably, the pH of an intravenous formulation ranges from about 6-8, more preferably from about 7-8 and most preferably at or about physiological pH (e.g., about 7.2-7.6).
Hence, there has been an on-going search for compounds that exhibit not only increased potency against resistant strains but also the physicochemical and pharmacological characteristics that enhance the effectiveness of a candidate compound and which may determine ultimately its acceptance in the clinic and resulting commercial success.